Method of and apparatus for the electrochemical treatment of work surfaces

ABSTRACT

A method and apparatus for the electrochemical treatment of work surfaces is disclosed. The method includes placing an electrolytic solution in contact with a suitable membrane. The solution passes through the membrane in a first direction to contact the work surface to be treated. A current is passed through the solution and the workpiece to polarize the ions contained in the solution and to initiate an electrochemical reaction between the work surface and a first portion of the polarized ions, electrochemically reactive with the work surface. A second portion of the polarized ions, non-reactive electrochemically with the work surface passes through the membrane in a second direction, opposite the first direction, to assure a relatively rapid and uniform rate of electrochemical treatment. The apparatus comprises a container for the electrolytic solution to which is affixed the membrane, which acts as a dispensing member for the solution, and a voltage source for passing current through the solution and the work surface. A vibrator and/or pressure applier may be associated with the container to increase the dispensing rate of the solution through the membrane.

United States Patent 91 Kenney 1 Jan. 30, 1973 [75] Inventor: John Thomas Kenney, Lawrence Township, Mercer County, NJ.

[73] Assignee: Western Electric Company, Incorporated, New York, NY.

[22] Filed: Oct. 23, 1970 [21] Appl. No.: 83,474

[52] U.S. Cl ..204/15, 204/224 [51] Int. Cl. ..C23b 5/48, 823p 1/02 [58] Field of Search ..204/224, 15

[56] 1 References Cited UNITED STATES PATENTS 828,814 8/1906 Cunningham ..204/224 1,344,928 2/1932 Slepian -204/224 2,080,234 5/1937 Schlotter... .....204/224 2,108,700 2/1938 Adey ..204/224 2,540,602 2/1951 Thomas et a1. .....204/224 3,290,236 12/1966 Mayer ..204/224 2,491,910 12/1949 Schinske .....204/224 2,498,129 2/1950 Lindsay ..204/224 2,798,849 7/1957 Lindsay ..204/224 3,324,015 6/1967 Saia et al. ..204/224 FOREIGN PATENTS OR APPLICATIONS 810,475 3/1959 Great Britain ..204/140.5

VOLTAGE souacz Primary ExaminerJ0lm H. Mack Assistant Examiner-T. Tufariello Att0rney-W. M. Kain, R. P. Miller and R. C. Winter [57] ABSTRACT A method and apparatus for the electrochemical treatment of work surfaces is disclosed. The method includes placing an electrolytic solution in contact with a suitable membrane. The solution passes through the membrane in a first direction to contact the work surface to be treated. A current is passed through the solution and the workpiece to polarize the ions contained in'the solution and to initiate an electrochemical reaction between the work surface and a first portion of the polarized ions, electrochemically reactive with the work surface. A second portion of the polarized ions, non-reactive electrochemically with the work surface passes through the membrane in a second direction, opposite the first direction, to assure a relatively rapid and uniform rate of electrochemical treatment. The apparatus comprises a container for the electrolytic solution to which is affixed the membrane, which acts as a dispensing member for the solution, and a voltage source for passing current through the solution and the work surface. A vibrator and/or pressure applier may be associated with the container to increase the dispensing rate of the solution through the membrane.

14 Claims, 4 Drawing Figures PATENTEUJAH 30 I973 SHEEI 2 BF 2 VIBRATOR PRESSURE SOURCE VOLTAGE SOURCE VIBRATOR VIBRATOR PRESSURE SOURCE VOLTAGE SOURCE METHOD OF AND APPARATUS FOR THE ELECTROCHEMICAL TREATMENT OF WORK SURFACES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method of and apparatus for the electrochemical treatment of workpieces, and

more particularly, to a method of and apparatus for the selective electrochemical treatment of workpieces with a liquid electrolyte.

2. Description of the Prior Art Often it is necessary or desirable to electrochemically treat workpieces. Such treatment may involve plating, etching, anodizing or the like, and may be ef fected on either all or only on selected portions of the workpiece. Two general techniques have previously been used to effect electrochemical treatment. The first is a masking technique and the second is a selective electrolyte placement technique. Both techniques employ an electrolyte, placed in contact with the workpiece, and the passage of a current therethrough.

In the masking technique the workpiece is masked and is then treated by exposing portions thereof not covered by the mask to a liquid electrolyte. Electrolyte exposure may be effected either by local application of the electrolyte to the uncovered workpiece portions or by so called tank processing wherein the masked workpiece is immersed in a bath of the electrolyte. This technique is time consuming and costly, because the masking steps must be accurately effected prior to and in addition to other production procedures. Moreover, the mask must usually then be removed.

At times the articles which are to be electrochemically treated are either too large or unwieldy to utilize the masking technique especially where tank processing is employed. Accordingly, selective electrolyte placement may be used. In a first type of selective electrolyte placement, an electrolyte in solid or viscous form is applied to selected portions of workpiece in a pattern, and electrical current is then passed through the electrolyte pattern to polarize the electrolyte into ions and to achieve the desired electrochemical treatment. This latter technique is somewhat undesirable because of 1) slow electrochemical reaction rate due to long migration time of those ions reactive with the workpiece, (2) fluctuations in the voltage across the electrolyte patterns, again due to the long migration time of the reactive ions, and (3) irregular electrochemical treatment across the surface of the workpiece due to uneven migration of the reactive ions.

In a second type of selective electrolyte placement a probe or dispenser is employed which both dispenses the electrolyte to a workpiece and the surfaces thereof to be selectively electrochemically treated and acts as either a cathode or an anode in an electrochemical reaction. However, most of these apparatus and the methods they employ depend largely upon capillary action to pass the electrolyte to the surfaces through an applicaton such as a pad or wick which is affixed to the dispenser. There are many problems and disadvantages inherent in such apparatus and methods. One such problem is that the rate of the electrochemical reaction is very much slower than the rate of the same electrochemical reaction achieved through electrolytic bath and immersion techniques. This slower rate is due to long migration of the electrolyte through the long thin capillary paths. A second problem is that during the electrochemical treatment of the workpiece, electrochemically reactive ions contained in the dispensed electrolyte electrochemically react with the workpiece leading to a deficiency of reactive ions. The concentration of the reactive ions can thereafter only be replenished through the natural diffusion of the reactive ions from the body of the electrolytic solution. At the same time, however, electrochemically unreacted ions accumulate at the surface of the workpiece thereby inhibiting the diffusion of the reactive ions to the surface site and thus resulting in an impediment of the reaction rate. An apparatus wherein these unreacted ions or a portion thereof can be removed from the reaction surface site is therefore desirable, since with a wick or pad dispenser a reverse capillarity encompassing this removal usually does not occur.

A third problem is that if gas bubbles are given off during the electrochemical treatment, these bubbles often passivate the surface of the workpiece towards further reaction since they cannot adequately pass through the pads or wicks and may even inhibit the capillary action thereof. Also a nonuniformity of electrochemical reaction due to uneven application of electrolyte flowing through the wick often occurs and, lastly, large fluctuations in voltage are encountered during the electrochemical treatment. Therefore, a method and apparatus which can obviate the aboveenumerated problems has long been sought.

SUMMARY OF THE INVENTION The present invention is directed to a method and apparatus for selectively treating portions of a workpiece electrochemically. The apparatus consists of an electrically inert -or dielectric container for housing a suitable electrolyte or electrolytic solution. At one end of the container is a membrane affixed thereto by suitable means and through which isdestined to pass the electrolyte contained within the container. Passing through a wall of the container and extending into the electrolyte is an electrode which may be connected by suitable means to an external voltage source either an an anode or as a cathode. At the opposed or open end of the container may be affixed by suitable means a cover plate which may have a pressure creating source attached thereto for aiding the passage of the electrolyte through the membrane. To the container there may also be affixed a vibratory means for aiding the passage of the electrolyte through the membrane.

In operation a suitable workpiece, having conductive surfaces is selected. The conductive workpiece is connected by suitable means to one polar side of an external voltage source thereby making the workpiece either the cathode, e.g., when plating thereupon is desired, or anode, e.g., when the workpiece is to be anodized. The container of the assembled apparatus is placed above the area of the workpiece to be selectively, electrochemically reacted upon. A suitable electrolyte, i.e., one selected either for electrochemical plating, etching or anodization, is placed within the container thereby contacting and permeating the membrane. The electrode passing through the container and maintained within the electrolyte is charged or polarized opposite to that of the workpiece, i.e., it is affixed to the other pole of the external voltage source. The electrolyte passes through the membrane to the workpiece at a controlled uniform rate, which may be increased by the pressure creating source affixed to the cover plate of the container, and a uniform, relatively rapid electrolytic reaction takes place at a constant rate which is not impeded through surface depletion mechanisms or surface impediments, such as, gas bubbles.

The method and'apparatus is one which optimizes selective electrochemical treatment of work surfaces by:

l. achieving an electrochemical reaction rate which approaches that of an electrochemical bath operation;

2. maintaining the surface depletion of active ions, i.e., those ions capable of electrochemically reacting with the work surface, during the electrochemical reac tion to a minimum;

3. dissipating bubbles from the workpiece surface which may form during the electrochemical reaction thereby assuring uniform electrochemical reaction;

4. depositing a microscopically thin, i.e., not observable to the naked eye, uniform electrolyte layer to the selected surface thereby assuring uniformity of electrochemical action across the surface of the workpiece; and

5. maintaining voltage drops or fluctuations during the electrochemical treatment to a minimum.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more readily understood by reference to the following drawing taken in conjunction with the detailed description, wherein:

FIG. 1 is a perspective view of the novel apparatus of the invention used to carry out the novel method of the DETAILED DESCRIPTION The present invention is described primarily in terms of the electrodeposition of a metal on a suitable workpiece or substrate and of the anodization of a substrate. However, it should be understood that such description is exemplary only and is for purposes of exposition and not for purposes of limitation. It will be readily appreciated that the inventive concept described is equally applicable to all types of electrochemical reactions, such as, electroetching, electropolishing, anodizing, as well as electroplating. Also, the inventive concept described is applicable to the many permutations and combinations of electrolyte, substrate, and electrode utilized in the vast field of electrochemistry.

With reference now to FIG. 1, there is shown the electrochemical treatment apparatus of the present invention. Shown in the figure is a container 31, destined for containing a suitable electrolyte or electrolytic solution 32. The container 31 may be fabricated from any material which is electrically and chemically inert, i.e., any dielectric or nonconductor, such as certain glasses and plastics, which is inert to the suitable electrolytic solution 32 selected. As illustrated in FIG. 1, the container 31 may be cylindrical in shape, but this is for illustrative purposes only and the invention is not to be restricted thereby for the container 31 may be rectangular or even parallelepiped in shape. In this regard, it should be noted that the container 31 may be either of a resilient or rigid construction and may be of a size so as to be hand manipulative.

Affixed to the lower end of container 31 by any suitable means, which is inert electrically and to the electrolyte chosen, as for example by a nylon thread, glues or cements, is a suitable membrane 33. A suitable membrane consists of a nonconductive material which has pores which permit the passage of the desired ions of the electrolyte 32 chosen and also permit the passage of small molecules, such as water, in small amounts rather than permitting bulk flow passage. The membrane, in other words, may be made of any material, such as a plastic film, e.g., a regenerated cellulose film, which permits the passage of desired ions. It should be noted here, that the particular membrane selected is chosen, in regard to the electrolytic solution 32 involved, so as to create a controlled dispensing rate or rate of passage of the electrolytic solution 32 to a particular work surface which is to be electrochemically treated. The membrane selected should have a pore size which permits the electrolytic solution to be dispensed to the particular work surface so as to form a microscopically thin, uniform electrolytic film, not observable to the naked eye, on the particular surface.

Affixed to and passing through a wall of the container 31 into the electrolytic solution 32 is a suitable electrode 34. A suitable electrode is one which is selected for its functionability with the electrolytic solution 32 with respect to the electrochemical reaction desired, i.e., either for electroplating, electroetching, or anodizing. The electrode 34 is connected by suitable means 36 to a pole or one polar side of a standard voltage source 37, e.g., a battery. Whether the electrode 34 is connected to the positive side or the negative side of source 37 is determined by the electrochemical reaction to be performed, i.e., whether electrode 34 is to function as an anode or a cathode.

Aftixed to and covering the upper end of container 31 may be a cover plate 38, which is fabricated from the above-mentioned dielectric material, for confining the electrolytic solution 32. Also an inlet means 39 may pass through cover plate 38. Through the inlet means 39 may be passed a pressurized inert gas from a standard pressure source 41. The use of a slightly pressurized gas permits the electrolytic solution 32 to pass through membrane 33 at a more rapid rate. However, the use of a pressurized gas and its accompanying inlet means 39 is for illustrative purposes only and the inventive embodiment need not be restricted thereby. In the alternative, the container 31 may be fabricated ofa pliable, flexible material whereby container 31 may be compressed so as to produce the constant increased pressure desired. However, it is important to note that the inventive embodiment need not require a presployed. In this regard it should be noted that where a pressure of 2 lbs./in. is employed, adequate flow rates are obtained with membranes having a pore size ranging from 0.45 5.0 a. It should also be noted here that the membrane 33 may be presoaked for a period of time in a suitable solvent or solution, e.g., glycerin in water for cellulose membranes, to render it more pliable and flexible.

The above-described apparatus can be employed for the electrochemical treatment of suitable workpieces. Referring to FIG. 2, container 31, in operation is placed above a suitable substrate material or workpiece 42, i.e., a material capable of conducting electricity. The workpiece 42 is attached by a suitable means 43 to the external voltage source 37. The container 31 is placed over that region or section 42(a) of the workpiece 42 which is to be electrochemically treated. The container 31 is filled with a suitable electrolytic solution 32 which contacts membrane 33. A suitable electrolytic solution is one which is dependent upon the workpiece material 42 and upon the electrochemical reaction desired to be performed on the workpiece section 42(a).

The electrode 34 and the workpiece 42 are both attached to opposite poles of the voltage source 37 and each may be charged anodically or cathodically with respect to one another. The membrane 33 is selected so as to uniformly dispense the electrolytic 32, i.e., the membrane selected is such that the electrolytic solution 32 permeates the membrane 33 and passes therethrough to section 42(a) of the workpiece 42 at a uniform and constant rate. The electrolytic solution 32 passes through membrane 33 in a first direction to form a microscopically thin, uniform layer of electrolyte 32(a) on the membrane 32, which solution layer 32(a) contacts section 42(a). It should be noted that layer 32(a) is microscopic, i.e., not visible to the naked eye, and that for illustrative purposes only, layer 32(a) has been magnified in FIG. 2. The electrical circuit is now completed by passing current from the voltage source 37 to the electrode 34 charged either as the cathode or anode, which current is carried by the dissociated and now polarized ions of the electrolytic solution 32 and of layer 32(a) to the oppositely charged workpiece 42 whereby the electrochemical reaction desired is initiated.

When the electrolytic solution 32 passes through membrane 33 in a first direction the following occurs sequentially:

l. a thin microscopic and uniform layer of electrolyte 32(a) contacts and forms over area 42(a) of workpiece 42 thereby assuring that all surface portions of areas 42(a) are destined to be subjected to a uniform electrolytic or electrochemical action;

2. the electrical circuit is completed whereby the ions contained in electrolytic solution 32 and layer 32(a), are polarized, i.e., the negative ions continually migrate to the anode and the positive ions migrate to the cathode;

3. a portion of those polarized ions, contained in electrolyte layer 32(a) capable of electrochemically reacting with the cathodically or anodically charged workpiece 42, electrochemically react with area 42(a) of workpiece 42 to initiate the desired electrochemical reaction;

4. a portion of those polarized ions contained in layer 32(a), which are non-reactive electrochemically with the charged workpiece 42, pass through the membrane 33 in a second direction, opposite the first direction and away from the workpiece 42.

The rate of the resultant reaction is relatively rapid and uniform and one which approximates the rates achievable through a dipping or electrolytic bath technique because, (i) the permeable nature of membrane 33 and the microscopic thinness of layer 32(a) leads to a voltage drop thereacross which is quite small and does not fluctuate, (ii) the portion of those polarized ions which does not electrochemically react with surface 42(a) of workpiece 42 passes through the membrane 33 in the second direction, opposite the first direction through which the electrolyte solution 32 passes, thereby preventing surface depletion of reactive ions at surface 42(a), and (iii) gas bubbles which may form during the electrochemical treatment of the workpiece 42 pass from surface 42(a), through the membrane 33 in the second direction, to minimize surface impediments to the electrolytic reaction at surface 42(a).

Referring to FIG. 2, in order to speed the flow rate of the solution 32 through membrane 33 to form layer 32(a), vibratory means 40, e.g., a transducer, may be affixed either to container 31 or the workpiece 42 or to both to apply vibratory agitation to solution 32 and layer 32(a), thereby increasing the passage through membrane 33 in both the first and second direction. It has been found, that the vibratory means is effective at frequencies ranging from 50 H, to the ultrasonic region, i.e., in the order of 200,000 H However, the use of vibratory means is for illustrative purposes only and the inventive embodiment need not be restricted thereby since a membrane may be selected so as to give the flow rate desired.

In another embodiment of the invention, a suitable mask 44 fabricated of any inert, hydrophobic material incapable of being plated upon is placed over the workpiece 42, as shown in FIG. 3A. Unlike prior masking techniques, the mask 44 may be repetitively employed without destruction thereof and may be quickly applied over the workpiece 42 to achieve selective electrolytic reaction thereupon. The mask 44 has apertures 46 therein which correspond to the areas 42(b) and 42(0) of the workpiece to be electrochemically treated. The container 31 containing the suitable electrolytic solution 32 is placed upon the mask 44. The electrode 34 and the workpiece 42 are connected to opposite poles of the voltage source 37 by means 36 and 43, thereby completing the electrical circuit from the electrode 34, the electrolytic solution 32, microscopic electrolyte layers 32(b) and 32(c) destined to be formed by the passage of solution 32 through membrane 33 (FIG. 3B) and the workpiece 42. Pressure is introduced into container 31 by means of the pressure source 41 through the inlet 39 of cover plate 38. In this regard, the external pressure introduced, e.g., by pressurized gas, is in the range of l to 4 lbs/inch.

Referring to FIG. 3B, the externally introduced pressure forces the flexible membrane 33 to distort and contour to apertures 46 of mask 44. The electrolytic solution 32 permeates and passes through the contoured portions of membrane 33 in a first direction at a uniform constant rate whereby the following occurs sequentially:

1. thin and uniform microscopic layers 32(b), 32(c), of electrolyte 32 form over areas 42(b) and 42(c) of workpiece 42 thereby assuring that these areas are destined to be subjected to a uniform electrolytic action;

2. the electrical circuit is completed and current is passed through the substrate 42 and the electrolyte 32, 32(b) and 32(c), whereby the ions contained electrolytic solution 32 and layers 32(b) and 32(c) are polarized;

3. a portion of the polarized ions contained in electrolyte layers 32(b) and 32(c), electrochemically reactive with the charged workpiece 42, electrochemically react with areas 42(b) and 42(c) of workpiece 42 to initiate the desired electrochemical reaction;

4. a portion of those polarized ion contained in layers 32(b) and 32(c), which do not electrochemically react with surfaces 42(b) and 42(c) of charged workpiece 42, pass through the contoured portions of membrane 33 in a second direction, opposite the first direction and away from the workpiece 42, thereby minimizing surface depletion of the active ions at the surfaces 42(b), 42(c) to maintain the rate of reaction relatively rapid and uniform; and

5. gas bubbles which may form during the electrochemical treatment of the workpiece 42 pass from surfaces 42(b) and 42(c) through the contoured sections of membrane 33 in the second direction to minimize surface impediments to the electrolytic reaction at the surfaces 42(b) and 42(c), thereby assuring a relatively rapid and uniform rate of reaction.

Again, it should be noted that layers 32(b) and 32(c) are microscopic, i.e., are not visible to the naked eye, and that for illustrative purposes only, layers 32(b) and 32(0) have been magnified in FIG. 38. Also, referring to FIGS. 3A and 38, a vibratory means 40, e.g., a transducer, may be affixed either to container 31 or the workpiece 42 or to both in order to speed the flow rate of the solution 32 through membrane 33. Again, it should be noted that this is for illustrative purposes only and the inventive embodiment need not be restricted thereby.

EXAMPLEl To serve for comparison purposes with respect to electroplating, a 6 inch X 3 inch phenolic printed circuit board of the type well known in the art, having a top layer of metallic copper, was subjected to a brightcopper plating bath deposition, employing reagents and processes well known in the art. A bright-copper deposit of 100 microinches was plated on the top layer, whereupon the board was placed in a standard gold citrate plating solution contained within a glass beaker. A platinum electrode was placed within the plating solution and the bright-copper layer was rendered negatively with respect thereto. The solution was maintained at a temperature of 25 C and a current density of 3 amps/ft, whereupon a 200 microinch, gold layer was deposited upon the bright-copper layer after 25 minutes.

EXAMPLE [I A 6 inch X 3 inch phenolic printed circuit board, of the type well known in the art, having a top layer of metallic copper, was subjected to a bright-copper plating bath deposition, employing reagents and processes well known in the art. A bright-copper deposit of microinches was plated on the top layer.

An apparatus similar to that described in FIG. 1 was selected. The container 31 consisted of a 3 inch long glass tube having an outside diameter of 15 mm. and a wall thickness of 1 mm. A cellulose triacetate membrane 33, commercially obtained and having a pore size of 0.8 2, was affixed to the bottom of the glass container 31 by means of an epoxy cement, commercially obtained and well known in the art. A platinum electrode 34 was inserted through a wall of the glass tube 31 and sealed therein. A standard gold citrate plating solution 32, commercially obtained and well known in the art, was placed in the tube 31. A glass cover plate 38 having a glass inlet means 39 was placed at the top of tube 31. Affixed to the inlet means 39, by standard means known in the art, was a pressure source 41 consisting of a standard source of nitrogen gas maintained at a pressure of2 lbs./in.

The glass container 31 was placed above the substrate 42, i.e., above the bright-copper layer of the circuit board, in the manner illustrated. A transducer 40 was placed upon the substrate 42 whereby vibratory motion was imparted to the circuit board substrate 42. The substrate 42 was charged cathodically with respect to the electrode 34, i.e., the substrate 42 was connected by means 43 to the negative pole of a battery 37 and the electrode 34 was connected by means 36 to the positive pole of the battery 37. The pressurized nitrogen was admitted into the container 31 at a pressure of 2 lbs./in. whereafter the electrolytic plating solution 32 passed through the membrane 33 in a first direction into contact with the substrate 42. The following then occurred:

1. a thin, microscopic and uniform layer 32(a) of the plating solution 32 formed on the membrane 33, contacted and coated the substrate 42, i.e., a 15 mm. diameter circular layer, not visible to the human eye, was formed on a discrete region 42(a) of the brightcopper layer of the substrate 42;

2. the electrical circuit was completed whereby current was passed through the substrate 42 and electrolyte 32 and 32(a) and the ions contained in electrolyte 32 and 32(a) were polarized, i.e., all the positive ions, including H", Au began to migrate to the cathodic substrate 42 and all the negative ions started to migrate toward the anodic platinum electrode 34;

3. at the cathodic substrate 42, (i) a portion of those polarized ions contained in electrolyte layer 32(a), capable of electrochemically reacting with the substrate 42, (the positive ions), electrochemically reacted therewith so resulting in the reduction of the Au to Au and the H to H (ii) the resulting Au was deposited upon the substrate 42 at area 42(a) and the resultant H, gas passed through the membrane 33 in a second direction opposite the first direction and away from the substrate; and (iii) a portion of those'ions (negative ions) contained in layer 32(a) incapable of electrochemically reacting with the cathodic substrate 42 passed through the membrane 33 in the second direction.

The citrate plating solution 32 was maintained at a temperature 25 C and a current density of 3 amps/ft}. After 25 minutes a uniform, circular layer of gold was deposited which was 15 mm. in diameter and 100 microinches in thickness.

EXAMPLE III The apparatus and procedure of Example II was re peated except that the triacetate membrane had a pore size of 1.2a and the pressurized nitrogen gas was maintained and admitted into the system at 10 oz./in. of pressure. After 25 minutes a gold layer of 100 microincheswas obtained.

EXAMPLE IV The apparatus and procedure of Example II was repeated except that the membrane employed was a cellulose membrane, commercially obtained and capable of retaining compounds having molecular weights above 12,000. The cellulose membrane was pre-soaked for 24 hours in a 20 percent by weight aqueous glycerin solution in order to make it more flexible whereupon it was stretched over the bottom of the glass tube 31 and affixed thereto by means of a compression-type plastic collar. After 25 minutes a deposited gold layer of 130 microinches was obtained.

EXAMPLE V The apparatus and procedure of Example II was employed except that a polytetrafluoroethylene mask, similar to that described in FIG. 3A, was employed. The mask had a 5 mm. X mm. rectangular aperture therein. After 25 minutes a 5 mm. X 10 mm. rectangular gold deposit of 100 microinches was obtained.

EXAMPLE VI EXAMPLE VII A 6 inch X 3 inch tantalum foil was selected. Apparatus similar to that described in Example II was selected except that the solution 32 contained therein was 10 percent, by weight, aqueous H PO.,.

Referring to FIG. 2, the glass container 31 was placed above the substrate 42, i.e., the tantalum foil, in the manner illustrated. A transducer 40 was placed upon the substrate 42 whereby vibratory motion was imparted to the substrate 42. The substrate 42 was charged anodically with respect to the platinum electrade 34, i.e., the substrate 42 was connected by means 43 to the positive pole of a battery 37 and the electrode 34 was connected by means 36 to the negative pole of the battery 37. Pressurized nitrogen was admitted into the container 31 at a pressure of 2 lbs./in. whereafter the electrolytic anodizing solution 32 passed through the membrane 33 in a first direction into contact with the tantalum substrate 42. The following then occurred:

5 l. a thin microscopic and uniform layer 32(a) of the electrolytic solution 32 formed over the substrate 42, i.e., a mm. diameter circular layer, not visible to the human eye, formed on a discrete region 42(a) of the tantalum substrate 42;

2. the electrical circuit was completed whereby current was passed through the substrate 42 and the electrolyte 32 and 32(a), and the ions contained in electrolyte 32 and 32(a) were polarized, i.e., all the negative ions began to migrate to the anodic substrate 42 and all the positive ions began to migrate towards the cathodic platinum electrode 34;

3. at the anodic substrate 42, (i) a portion of those polarized ions contained in the electrolyte layer 32(a),

capable of electrochemically reacting with the substrate 42, (the negative ions), electrochemically reacted therewith so resulting in the oxidation of these ions and the oxidation or anodization of the tantalum substrate 42 at area 42(a), (ii) a portion of those ions (positive ions) contained in layer 32(a), incapable of electrochemically reacting with the substrate 42 passed through the membrane 33 in a second direction which is opposite the first direction and away from the substrate 42.

The I-l PO solution 32 was maintained at 25 C and an initial current of 225 111. amps. was introduced whereby the potential, measured across the substrate 42, went from an initial 10 volts to 150 volts in 35 seconds, i.e., a 150 volt oxide layer was obtained on the 35 tantalum substrate 42.

What is claimed is:

l. A method of electrochemically treating a conductive surface, which comprises:

a. contacting a cellulose membrane, having a pore size ranging from 0.45 p. to 5.0 1., with an electrolytic solution, said solution passing through said membrane to form a microscopically thin, uniform electrolytic solution layer on said membrane;

b. contacting a selected region of the conductive surface with said solution layer; and

c. passing a current through said solution and said region to electrochemically treat said region.

2. A method of electrochemically treating a conductive surface, which comprises:

a. contacting a cellulose membrane, having a pore size ranging from 0.45 to 5.011., with an electrolytic solution, said solution passing through said membrane in a first direction, to form a microscopically thin, uniform electrolytic solution layer on said membrane;

. contacting a selected region of the conductive surface with said solution layer;

0. passing a current through said solution and said region to (l) polarize ionscontained in said solution and, (2) electrochemically reacting a portion of said polarized ions, contained in said layer and electrochemically reactive with the conductive surface, with said region while a portion of said polarized ions, contained in said layer and nonreactive electrochemically with the conductive surface, passes through said membrane in a second direction, opposite said first direction and away from said region, whereby a relatively rapid and uniform rate ofelectrochemical treatment occurs.

3. The method as defined in claim 2 which further comprises the steps of:

a. confining said solution, and

b. applying pressure to said solution to increase the rate of passage of said solution in said first direction.

4. The method as defined in claim 2 which further comprises the step of vibrating said solution to increase the rate of passage of said solution in said first direction and the rate of passage of said non-reactive ion portion in said second direction.

5. The method as defined in claim 3 which further comprises:

a. contacting a mask, having an aperture therein,

with said solution layer;

b. contouring a portion of said membrane to said aperture; and

c. passing said solution layer through said membrane portion to contact said selected region with said solution layer.

6. A method for electrochemically treating a discrete region of a workpiece, which comprises:

a. forming a mask having an aperture corresponding to said discrete region;

b. placing said mask on said workpiece with said aperture over said discrete region;

0. contacting said mask with a cellulose membrane,

having a pore size ranging from 0.45;; to 5.0;;.;

d. contacting said membrane with a confined electrolytic solution;

e. applying pressure to said solution to contour a portion of said membrane to said aperture;

f. passing said solution through said membrane portion in a first direction to contact said discrete region and to form a microscopically thin, uniform solution layer on said region; and

g. passing a current through said solution and said workpiece to obtain an electrochemical reaction at said discrete region only.

7. The method as defined in claim 6 which further comprises the step of vibrating said confined solution to increase the rate of passage of said solution through said membrane portion in said first direction.

8. A device for electrochemical treatment of a work surface, which comprises:

a. means for containing an electrolytic solution;

b. a cellulose membrane, having a pore size ranging from 0.45p. to 5.0;]., affixed to said electrolytic solution containing means, for passing a microscopic layer of said solution in a first direction into contact with the work surface and for passing a portion of polarized ions, unreactive with the work surface and contained in said microscopic solution layer, in a second direction, opposite of said first direction and away from the work surface; and

c. means for applying a current to said solution and the work surface to polarize the ions of said solution and to react a portion of polarized ions, electrochemically reactive with the work surface and contained in said solution, with the work surface.

9. The device as defined in claim 8 wherein said cellulose membrane com rises cellulose triacetate.

10. The device as efined in claim 8 which further comprises a pressure means affixed to said containing means for increasing the rate of passage of said solution in said first direction.

11. The device as defined in claim 8 which further comprises a vibratory means contiguous to said containing means for increasing the rate passage of said solution in said first direction and the rate of passage of said portion of unreactive ions in said second direction.

12. In an improved device for the electrochemical treatment of a work surface of the type which includes a dielectric container, adapted to be grasped and manipulated by the operator for containing an electrolyte, an electrolyte dispensing member affixed to one end of said container for dispensing electrolyte to the surface to be treated, means for conducting electri-' cal current to the electrolyte and the surface to be treated, wherein the improvement comprises:

a cellulose membrane, having a pore size ranging from 0.45 1. to 5.0a, serving as said dispensing member for dispensing said electrolyte at a controlled rate in a microscopically thin, uniform layer and for preventing active ion depletion at the treated surface.

13. The device as defined in claim 12 which further comprises a pressure means affixed to said dielectric container for increasing the rate of dispensing said electrolyte.

14. The device as defined in claim 12 which further comprises a vibratory means contiguous to said dielectric container for increasing the rate of dispensing said electrolyte.

mm STATESPATEN? owes cs rimrr r 15cm Patent No. 3,713 99 v m Ja ary 3 973 lnventor(s) T. Kenney It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as, showri below:

Column 1, line 41, "of workpiece" should read -of a workpiece-. Column 2, lines #6 and 47, either an an" should read -either as an-.- Column 7, lines .13 and 14, "contained electrolytic should read contained in electrolytic'--5 line 22, ion should read-muons",

Column 10, claim 2, line 62, "reacting" should read --react-.

signed a Sealed this 10th y Qf r 1973.

' (SEAL) Attest EDWARD M.FLETCHER,,JR.

Rene Tegtmeyer Attesting Officer Acting Commissioner of Patents 

1. A method of electrochemically treating a conductive surface, which comprises: a. contacting a cellulose membrane, having a pore size ranging from 0.45 Mu to 5.0 Mu , with an electrolytic solution, said solution passing through said membrane to form a microscopically thin, uniform electrolytic solution layer on said membrane; b. contacting a selected region of the conductive surface with said solution layer; and c. passing a current through said solution and said region to electrochemically treat said region.
 2. A method of electrochemically treating a conductive surface, which comprises: a. contacting a cellulose membrane, having a pore size ranging from 0.45 Mu to 5.0 Mu , with an electrolytic solution, said solution passing through said membrane in a first direction, to form a microscopically thin, uniform electrolytic solution layer on said membrane; b. contacting a selected region of the conductive surface with said solution layer; c. passing a current through said solution and said region to (1) polarize ions contained in said solution and, (2) electrochemically reacting a portion of said polarized ions, contained in said layer and electrochemically reactive with the conductive surface, with said region while a portion of said polarized ions, contained in said layer and non-reactive electrochemically with the conductive surface, passes through said membrane in a second direction, opposite said first direction and away from said region, whereby a relatively rapid and uniform rate of electrochemical treatment occurs.
 3. The method as defined in claim 2 which further comprises the steps of: a. confining said solution, and b. applying pressure to said solution to increase the rate of passage of said solution in said first direction.
 4. The method as defined in claim 2 which further comprises the step of vibrating said solution to increase the rate of passage of said solution in said first direction and the rate of passage of said non-reactive ion portion in said second direction.
 5. The method as defined in claim 3 which further comprises: a. contacting a mask, having an aperture therein, with said solution layer; b. contouring a portion of said membrane to said aperture; and c. passing said solution layer through said membrane portiOn to contact said selected region with said solution layer.
 6. A method for electrochemically treating a discrete region of a workpiece, which comprises: a. forming a mask having an aperture corresponding to said discrete region; b. placing said mask on said workpiece with said aperture over said discrete region; c. contacting said mask with a cellulose membrane, having a pore size ranging from 0.45 Mu to 5.0 Mu ; d. contacting said membrane with a confined electrolytic solution; e. applying pressure to said solution to contour a portion of said membrane to said aperture; f. passing said solution through said membrane portion in a first direction to contact said discrete region and to form a microscopically thin, uniform solution layer on said region; and g. passing a current through said solution and said workpiece to obtain an electrochemical reaction at said discrete region only.
 7. The method as defined in claim 6 which further comprises the step of vibrating said confined solution to increase the rate of passage of said solution through said membrane portion in said first direction.
 8. A device for electrochemical treatment of a work surface, which comprises: a. means for containing an electrolytic solution; b. a cellulose membrane, having a pore size ranging from 0.45 Mu to 5.0 Mu , affixed to said electrolytic solution containing means, for passing a microscopic layer of said solution in a first direction into contact with the work surface and for passing a portion of polarized ions, unreactive with the work surface and contained in said microscopic solution layer, in a second direction, opposite of said first direction and away from the work surface; and c. means for applying a current to said solution and the work surface to polarize the ions of said solution and to react a portion of polarized ions, electrochemically reactive with the work surface and contained in said solution, with the work surface.
 9. The device as defined in claim 8 wherein said cellulose membrane comprises cellulose triacetate.
 10. The device as defined in claim 8 which further comprises a pressure means affixed to said containing means for increasing the rate of passage of said solution in said first direction.
 11. The device as defined in claim 8 which further comprises a vibratory means contiguous to said containing means for increasing the rate passage of said solution in said first direction and the rate of passage of said portion of unreactive ions in said second direction.
 12. In an improved device for the electrochemical treatment of a work surface of the type which includes a dielectric container, adapted to be grasped and manipulated by the operator for containing an electrolyte, an electrolyte dispensing member affixed to one end of said container for dispensing electrolyte to the surface to be treated, means for conducting electrical current to the electrolyte and the surface to be treated, wherein the improvement comprises: a cellulose membrane, having a pore size ranging from 0.45 Mu to 5.0 Mu , serving as said dispensing member for dispensing said electrolyte at a controlled rate in a microscopically thin, uniform layer and for preventing active ion depletion at the treated surface.
 13. The device as defined in claim 12 which further comprises a pressure means affixed to said dielectric container for increasing the rate of dispensing said electrolyte. 